The present invention concerns a capacitor formed with a thin ferroelectric film, a memory device using the capacitor and a capacitor for preventing unnecessary electromagnetic radiation for a CPU, or an on-chip capacitor for use in a circuit-mounted substrate and, more particularly, the invention relates to a ferroelectric memory device applicable to a non-volatile memory and a manufacturing method thereof.
(1) Conventional thin ferroelectric film capacitors have a laminate is structure consisting of a Pt upper electrode/ferroelectric layer (PZT)/Pt lower electrode as described, for example, in xe2x80x9cThin Ferroelectric Film Memoryxe2x80x9d (published by Science Forum (1995), p 227).
(2) Further, in xe2x80x9cMethod of Forming a Thin Filmxe2x80x9d described, for example, in Japanese Patent Unexamined Publication Hei 7-142600, a compound BaTiO3 is formed on a thin Pt film, while the crystal orientation of the thin Pt film is reflected therein as it is, thereby making it possible to easily control the orientation property of the thin ferroelectric film and control the degree of residual dielectric polarization.
(3) Further, in xe2x80x9cMethod of Manufacturing a Thin ferroelectric filmxe2x80x9d described, for example, in Japanese Patent Unexamined Publication Hei 7-57535, a thin film of a perovskite type ferroelectric composition is formed on a substrate, on which a thin film of a perovskite type oxide composition solid solubilizable with the thin film of the perovskite type ferroelectric composition is formed, and a thin film comprising two layers consisting of a thin film of the ferroelectric composition and a thin film of the perovskite type oxide composition is subjected to a heat treatment to solid solubilize and crystallize them, to attain a method of manufacturing a thin ferroelectric film free from the formation of other phases than the perovskite phase and with a uniform crystal grain size.
The conventional capacitor described above in publication (1) involves a problem that the ferroelectric property thereof has a film thickness dependence and no sufficient characteristic can be obtained at a film thickness of 200 nm or less.
Further, as a problem inherent to the thin ferroelectric film capacitor, there is a film fatigue problem in that the dielectric polarizing characteristic is degraded and writing can not be accomplished with repeated reversion of the dielectric polarization many times, as well as an imprinting phenomenon which occurs when it is left polarized in one direction for a long time without conducting rewriting.
Further, the methods described in (2) and (3) involve a problem in that two kinds of thin films of perovskite crystals of quite different compositions have to be formed and this complicates the film-forming apparatus.
An object of the present invention is to provide a ferroelectric memory device which is subject to less film fatigue and imprinting and which has a long life, as well as a method of manufacturing such a device.
The object of the present invention can be attained by using a Pt electrode as an upper electrode of a thin ferroelectric film capacitor, and by disposing a metal or metal oxide electrode containing TiN, Pt, Ir or Ru above the Pt electrode as an upper protection electrode. Decomposed gases, which have evolved from materials present in the upper electrode or the wiring layer and the insulation layer formed on the upper protection electrode and which are present in the encapsulation resin in absorbed or interrupted form, serve to prevent degradation of the crystal structure caused by reduction, decomposition or formation into amorphous forms of the ferroelectric material and prevent lowering of the residual dielectric polarization value Pr. This can provide a ferroelectric memory device of high quality with a residual dielectric polarization value Pr between the upper electrode and the lower electrode of the capacitor of 1E-6C/cm2 or more, by heating, for example, to a temperature of 85xc2x0 C. or higher, maintaining the temperature for more than 90 min, then lowering the temperature to room temperature, applying a bias voltage of 1.0V to 3.5V between the upper electrode and the lower electrode, and then reducing the bias voltage to 0 V after manufacturing at least the wiring layer and the protection layer of the ferroelectric memory device, or, in addition, after encapsulating them in a package using a encapsulation resin, as an acceleration test for inspecting the reliability.
Further, the foregoing object can be attained by forming a barrier layer comprising SiO2 or Si3N4 above the upper electrode or the upper protection electrode of the thin ferroelectric film capacitor, reducing the number of hydrogen atoms contained in hydrocarbon compounds bonded to the barrier layer to 2.5E 17/cm2 or less, thereby reducing hydrogen evolved from the inside of the barrier layer during the processing step, and, further, chemically absorbing or physically interrupting decomposed gases evolved from the materials included in the protection layer and the wiring layer formed on the upper electrode and present in the encapsulation resin, thereby preventing degradation of the crystal structure caused by reduction, decomposition or formation into of the ferroelectric material into an amorphous form and preventing lowering of the residual dielectric polarization value Pr.
Further, the foregoing object can be attained by forming the barrier layer by a sputtering method or a laser abrasion method, reducing the partial pressure of hydrogen present in the atmosphere during the film-forming upon forming the barrier layer, and decreasing the impurity hydrocarbons contained in the barrier layer, thereby preventing degradation of the crystal structure caused by reduction, decomposition or formation the ferroelectric material into an amorphous form and preventing lowering of the residual dielectric polarization value Pr.
Further, the foregoing object can be attained by a method comprising a step of forming a thin amorphous film and a crystallizing step using heat treatment in oxygen as a step of manufacturing a thin ferroelectric film of the thin ferroelectric film capacitor, removing the surface layer of the thin ferroelectric film at least by nm using an ion etching method after the crystallizing step and forming the film of the upper electrode while keeping the ferroelectric film in a vacuum without exposing it to atmospheric air, thereby decreasing a modified layer at the boundary between the ferroelectric film and the upper electrode and thereby preventing lowering of the residual dielectric polarization value Pr.
Further, the foregoing object can be attained by a thin ferroelectric film capacitor having a laminate structure comprising, on a substrate, at least a lower electrode, a thin Pb(Zr, Ti)O3 film and an upper electrode in which a Pb excess ferroelectric layer is disposed at the boundary between the lower electrode and the thin ferroelectric film, and the compositional molar ratio of the Pb excess ferroelectric layer is defined as:
Pb:Zr:Ti:0=(1+y):(1xe2x88x92x):x:(3xe2x88x92z)
(0 less than y less than 0.3, 0.3 less than x less than 0.7, xe2x88x920.1 less than z less than 0.1),
thereby previously compensating the amount of Pb in the ferroelectric material at the electrode boundary upon diffusion into the electrode or reaction with the electrode.
Further, the foregoing object can be attained by forming a thin ferroelectric film layer without exposing the substrate to atmospheric air after the step of forming the lower electrode for forming a thin film of the lower electrode on the substrate in a vacuum vessel.
Further, the foregoing object can be attained by irradiating UV-rays in an oxygen atmosphere between the step of forming the lower electrode and the step of forming the thin ferroelectric film, during the manufacture of the thin ferroelectric film capacitor, thereby removing organic contaminates on the surface of the lower electrode.
Further, the foregoing object can be attained by forming the thin ferroelectric film in a vacuum, and forming a Pb excess ferroelectric layer by controlling the substrate temperature in the film-forming step, thereby controlling the Pb composition in the ferroelectric material.
Further, the foregoing object can be attained by a method comprising a step of preparing a thin ferroelectric film by a sputtering method, and forming a Pb excess ferroelectric layer by controlling the gas pressure or the electric power applied in the film-forming step, thereby controlling the Pb composition in the ferroelectric material.
Further, the foregoing object can be attained by a method comprising a step of preparing a ferroelectric thin film by a sputtering method, using a sintered mixture only composed of a ferroelectric material and a lead oxide as a target in the film-forming step and, further, defining the average crystal grain size of the target as 100 nm or more.
Further, the foregoing object can be attained by a method comprising a step of preparing the thin ferroelectric film by a multi-cathode type sputtering method in the step of preparing the thin ferroelectric film capacitor, using a sintered ferroelectric material as a first target in the film-forming step, further using a sintered lead oxide as a second target, and forming a Pb access ferroelectric layer by varying the electric power applied on every target in the film-forming step, thereby controlling the Pb composition in the ferroelectric material.